1. Technical Field
This invention relates to an optical recording medium initializing method and apparatus for initializing a rewritable recording medium by applying a light beam to the medium.
2. Background Art
Recently, rewritable recording media such as phase change type optical disks and magneto-optical disks have been employed in the art. Such recording media must be initialized when shipped to market. For this purpose, manufacturers of such recording media are provided with an optical recording medium initializing apparatus.
A conventional initializing apparatus is shown in FIG. 3(a). In the apparatus, a recording mechanism 1 is set on a turntable 2, which is rotated by a rotating mechanism such as a spindle motor 3. The spindle motor 3 is mounted on a bearing mechanism such as feed stage 4. The feed stage 4 is penetrated by the output shaft 6 of a conveying mechanism such as conveying motor 5. More specifically, the shaft 6 has a threaded portion 6a, which is engaged with a threaded portion (not shown) of the feed stage 4. The feed stage 4 is movably engaged with rails (not shown) on a supporting stand 7.
A conveying signal forming unit, such as a DC source 8, applies a conveying signal E to the conveying motor 5 to rotate the latter at a constant speed. As the conveying motor 5 rotates, that is, as the shaft 6 rotates, the feed stage 4 is moved in parallel with the shaft 6, or in the direction of the arrow X, at a constant speed due to the engagement of shaft 6 with the feed stage 4.
An irradiating mechanism, such as an optical unit 10, applies an initializing light beam 9 to the disk 1. The light beam 9 is moved in the direction opposite to the direction of the arrow X as the feed stage 4 is moved in the direction of the arrow X. Thus, the light beam 9 is moved relative to the disk 1. More specifically, the beam spot S of the light beam applied to the disk 1 is moved radially outwardly of the disk 1 along the axis A-B (as shown in FIG. 3(b), while the disk 1 continues to rotate. As a result, the beam spot S is moved in one direction in parallel with the shaft, and the whole surface of the disk can be initialized.
In order to shorten a period of time required for the initializing operation, the lens 10a of the optical unit 10 employs a lens 10a having a small numerical aperture (NA); that is, the beam spot of the light beam is made relatively large in diameter, about 20 .mu.m. Information recording track guides, such as pre-grooves, are provided on the disk 1. As shown in FIG. 4, the beam spot S is applied to a wide range of surface area including a number of pre-grooves. If the lens 10a is a cylindrical lens, the resultant beam spot S takes the form of an ellipse elongated in the direction X as shown in FIG. 5. Thus, the utilization factor of the light beam is increased as much.
The conveying signal E supplied to the conveying motor 5 is a DC voltage as shown in FIG. 6. Therefore, the feed stage 4 can be continuously moved parallel at a constant speed. However, since the disk 1 is rotated, the positions of the beam spot S in a radial direction are not continuous, as shown in FIG. 7. More specifically, the beam spot S is applied at intervals of .DELTA.x as indicated at S1, S2, S3 and so forth every revolution of the disk 1. The distance .DELTA.x can be represented by the following equation: EQU .DELTA.x=2.pi.v/.omega.
where v is the speed of movement of the feed stage 4, and .omega. is the angular speed of the disk 1.
The energy distribution of the light beam 9 is a Gaussian distribution and, therefore, the energy around the beam spot S is smaller than the energy at the center. Accordingly, the recording surface of the disk is not uniformly irradiated with the light beam; that is, the optical energy applied to the recording surface of the disk is not uniform in distribution as indicated in FIG. 7. Thus, it is impossible to suitably initialize the disk with the conventional initializing apparatus.